I tested the twin-threshold model, a risk-sensitive foraging model incorporating both a starvation threshold and a higher reproductive threshold. The model predicts risk-adverse foraging when an animal's energy state is close to the starvation threshold and risk-prone foraging when the animal's energy state is close to the reproductive threshold. Wild rufous hummingbirds (Selasphorus rufus) were presented with a choice of three artificial flower types that had either no, moderate or high variability around a common mean. I manipulated energy state by changing either the mean nectar volume or altering the cost of foraging (long versus short corollas). When the energy state of hummingbirds was close to the reproductive threshold they preferred the variable options. When the energy state of hummingbirds was close to the starvation threshold they preferred the nil option. Hummingbirds responded in a manner consistent with the twin-threshold model.

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Lethbridge, Alta. : University of Lethbridge, Faculty of Arts and Science, 2005